<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #parent{
            height: 400px;
            width: 400px;
            display: table-cell;
            text-align: center;
            vertical-align: middle;
            border: 1px solid black;
        }
        #childTwo{
            width: 100px;
            height: 100px;
            margin: auto;
            background-color: red;
        }
    </style>
</head>
<body>
    <div id="parent">
        <div id="childTwo">box</div>
    </div>
</body>
</html>